About me

I am a parasitologist. I have spent twenty years studying one organism, and I still find it astonishing.

I am Jeroen Saeij, a professor in the Department of Pathology, Microbiology and Immunology at the University of California, Davis, School of Veterinary Medicine. My lab studies Toxoplasma gondii, a single-celled parasite that infects roughly a third of all people and almost every warm-blooded animal on earth.

The short version

• I grew up in the Netherlands and did my PhD at Wageningen University, on how fish defend themselves against parasites.
• As a postdoctoral fellow with John Boothroyd at Stanford, I switched to Toxoplasma. We found that the parasite injects its own enzymes into the cells it invades in order to take control of them, and that small differences in those enzymes explain why some strains are far more dangerous than others.
• I started my own lab at MIT in 2007 and moved it to UC Davis in 2015.
• Along the way I became a Pew Scholar in the Biomedical Sciences, and the lab has published about a hundred peer-reviewed papers.

What my lab works on

We ask how Toxoplasma establishes itself inside a host and why the outcome differs so much between hosts and between parasite strains. That means finding the proteins the parasite secretes into our cells, working out how the immune system kills the parasite and how the parasite escapes, and explaining why strains common in South America cause severe eye disease in otherwise healthy people. Much of this now runs on genome-wide CRISPR screens, in which we switch off every parasite gene in turn to see which ones matter.

The details, the people and the papers are on my lab’s website at UC Davis and on PubMed.

Why this site exists

Two kinds of questions reach me again and again.

The first come from people who have just heard the word toxoplasmosis: someone who is pregnant and owns a cat, someone with a positive blood test, someone who read that a parasite controls their mind. Good answers exist, but they are scattered across the scientific literature and written for specialists. The toxoplasmosis pages are my attempt to give those answers plainly.

The second come from fellow scientists who run experiments for a living and now find that powerful computational tools are one download away. The tools are wonderful, and they are very good at producing convincing nonsense. The field guides collect what I have learned about telling the two apart.

How this site relates to my university work

This is a personal website. I write it in my own time, and it is not a publication of the University of California. Nothing here speaks for the university, and the opinions are mine. Some pages may eventually carry advertising or offer a paid guide. When they do, it will be clearly marked.

I cannot give personal medical advice. If you are worried about your own health or a pregnancy, please talk to your doctor.

Contact

You can reach me at hello@saeij.com.